1. Field of the Invention
The present invention relates to a compound semiconductor and a device thereof suitable for an infrared ray detector and a fabrication method thereof.
2. Description of the Related Art
A compound semiconductor device having a narrow energy gap is used for an infrared ray detector using, for example, indium antimonide (InSb). However, since the energy gap of indium antimonide is 0.17 eV, which is constant, the wavelengths of infrared rays that can be detected are restricted to approximately 5 .mu.m or less. As another compound semiconductor, mercury cadmium telluride (Cd.sub.x Hg.sub.1-x Te) is known. In the mercury cadmium telluride semiconductor, when x of Cd.sub.x Hg.sub.1-x Te is varied, the energy gap can be changed in the range from 0 to 1.6 eV. In particular, when the composition ratio x of cadmium is around 0.2, the energy gap becomes 0.1 eV. Thus, a compound semiconductor having an infrared detecting function of around 10 .mu.m band can be obtained.
However, the mercury cadmium telluride (Cd.sub.x Hg.sub.1-x Te) is composed of Hg and Cd, which are elements of group II, and Te, which is an element of group VI. In addition, the chemical bonding strength among these elements is weak. Moreover, mercury is thermally unstable. Thus, with these elements, it is difficult to fabricate homogeneous semiconductors with high reproducibility. Consequently, such a compound semiconductor device is not practically used. In reality, in a Cd.sub.x Hg.sub.1-x Te layer that is epitaxially grown, defects are present on the order of 10.sup.5 to 10.sup.8 cm.sup.-2 as EPD (Etch Pit Density) and fixed electric charges in a protective film are distributed in the range of .+-.10.sup.12 cm.sup.-2. Thus, the characteristics of the compound semiconductor tend to vary with temperature change. In addition, mercury of the composition elements has a problem in environmental conservation. Moreover, mercury should be handled and controlled with special care. Although the compound semiconductor device is attractive in characteristics, the utilization thereof is difficult.